Picture Exchange Communication System (PECS) is a picture-based communication strategy used to teach communication skills to persons with developmental disabilities including autism. This article systematically reviews 13 published single-subject studies to examine the effectiveness of PECS, the effects of PECS on speech and problem behaviors, generalization beyond training conditions, and social validity of the intervention. The authors also calculated percentage of nonoverlapping data points for all participants to quantify, compare, and analyze results. Results indicate that PECS yielded increases in functional communication in all but 1 participant. Additionally, PECS decreased problem behaviors and increased speech in some individuals. A theoretical framework, analyses of methodologies, and implications for researchers and practitioners are discussed. (Contains 2 tables.)